In conventional jaw crushers such as that manufactured by Protec Inc. and identified by the trade mark PIONEER 2148, the moving jaw is supported at its lower end by a plate which is commonly known as a toggle plate. Numerous attempts have been made to replace this toggle plate with a yieldable ram. One such device is described in U.S. Pat. No. 3,099,406, Kautz, dated July 30, 1963. In this device, overload protection is provided by employing a pneumatic damper in the control system. The problem with a pneumatic damper is that it is difficult to maintain a satisfactory seal in the pneumatic system over an extended period of time and further the pneumatic system will always tend to yield to a certain degree under the high impact loads required in order to effectively crush rock. As a consequence, it is necessary to set the pneumatic control pressure of a very high pressure. In addition, because the system combines both a pneumatic pressure system and a hydraulic pressure system, it is necessary to provide two separate power sources, one for supplying hydraulic fluid and the other for supplying pneumatic pressure. This complexity of equipment adds substantially to the cost of and the maintenance of rock crushing equipment.
It is an object of the present invention to provide a control system for controlling the movement of a movable jaw of a rock crusher which is fully hydraulic and which makes provision for accommodating overload conditions without damaging the jaws.
The control system of the present invention also permits the selective adjustment of the set position of the movable jaw.